Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality in the world. HCV is a major cause of HCC in the United States, Western Europe, and Japan and therefore it is critical to determine the molecular basis of the relationship between HCV and HCC. Published data show that viral point mutations in codons 70 and 91 of the HCV core gene are associated with the development of HCC, interferon (IFN) treatment failure, and insulin resistance. These viral mutations provide a compelling starting point for mechanistic studies of HCV-related hepatocellular carcinogenesis. We recently discovered that these mutations dramatically alter HCV gene expression and control the levels of two previously-unknown HCV proteins, 70 and 91 minicore proteins (Eng et al, 2009, J Virol). The proposed experiments examine the impact of these mutations, and two additional HCC-related HCV mutations that we identified (Fishman et al, 2009, Clin Cancer Res). The goal of Aim I is to determine whether core gene mutations arise prior to the development of liver cancer and thus could potentially promote hepatocellular carcinogenesis. A nested case-control study will be performed to compare core gene sequences of cases who developed HCC to those of controls who did not develop HCC during the Hepatitis C Antiviral Long-Term Treatment Against Cirrhosis (HALT-C) Trial. The primary outcome will be the percentage of cases versus controls in which the majority of the variants in the viral RNA population (i.e., the quasispecies) has a codon 70 mutation. Multivariable analysis will be performed to determine whether the codon 70 mutation is an independent predictor of incident HCC. Secondary outcomes will include associations between mutations in other codons and clinical outcomes, and changes in the quasispecies over time. The experimental goal of Aim II is to determine whether the HCC-related mutations confer a survival advantage to HCV during exposure to IFN in cell culture. Viral RNA and protein kinetics will be measured over time by qRT/PCR and Western blotting, using our established methods. These studies will determine the impact of four HCC-related mutations on HCV RNA replica- tion, protein synthesis (including minicore synthesis), and on the ability of HCV to withstand IFN treatment. The in vivo expression of minicores will be confirmed through analysis of liver specimens. This project challenges the paradigm, widely-held by investigators in the United States, that all HCV variants have an equivalent oncogenic potential. Accomplishment of our Aims will fill fundamental gaps in understand- ing the molecular basis of HCV-related oncogenesis and may lead to the identification of new targets for therapeutic interventions and to the development of diagnostic tests for patients harboring oncogenic variants. PUBLIC HEALTH RELEVANCE: The hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC), the third most common cause of cancer-related mortality in the world. Clinical studies indicate that point mutations in the HCV core gene enhance HCC risk and increase the likelihood of interferon treatment failure. Because of their clinical relevance, we will define the molecular effects of four HCC-associated mutations on viral replication, and also determine whether these mutations arise prior to HCC and therefore warrant investigation as possible biomarkers of virulent strains that can be used to identify patients who have an elevated risk of developing liver cancer.